In remote teleoperation of unmanned ground vehicles (UGVs), an operator uses a joystick to point sensors and steer the vehicle. Commands from these joysticks and other control devices are communicated to the UGV via radio waves or other systems generally known in the art. These control signals are received by the UGV and used to control the UGV and/or its sensors and payloads, generally referred to herein as “onboard subsystems.” Very often the onboard subsystem sampling rates required are greater than the sample rates that can be sent over a data link, and it is therefore necessary to perform a sample rate conversion. One typical application of sample rate conversion (SRC) may be performed (for example) onboard the UGV, as shown in FIG. 1. Operator 110 uses controller 120 to control UGV 130 via a wired tether or other means 140, including wireless communications systems known to one of ordinary skill in the art. Anti-aliasing filter 150 samples joystick 155 data at a sample rate of Fin and communicates the position input data to UGV 130 over link 140. Sample rate Fin is up-converted to the UGV's required sample rate Fout in converter 160 to control the onboard subsystems.
Sample rate conversions (SRC) of this sort are well known, as (for example) described in Schafer (Ronald W. Schafer and Lawrence R. Rabiner, “A Digital Signal Processing Approach to Interpolation,” Proceedings of the IEEE, vol. 61, no. 6, June 1973, pp. 692-702). Schafer considered the case of two-point linear interpolation and showed that the digital FIR implementation of the SRC has a triangular impulse response. Schafer also considered the general Lagrange interpolator and noted that for odd degree the filter was not linear phase. The Schafer reference, however, did not present a compact and configurable implementation for any of general Lagrange interpolations. Similarly, Ramstad (Tor A. Ramstad, “Digital Methods for Conversion Between Arbitrary Sampling Frequencies,” IEEE Transactions on Acoustics, Speech, and Signal Processing, vol. ASSP-32, no. 3, June 1984, pp. 577-591 has noted that when the SRC rate is rational, the coefficients required are periodic and can be precomputed. But this paper does not present any method for the generation of the coefficients.
In most cases of sample rate conversion, the group delay of the filter is less important than signal fidelity. However, in remote teleoperation it is desirable to keep the loop delay to a minimum to insure that the vehicle remains controllable, and the SRC filter group delay should also be made as small as possible.
One problem seen in the prior art is that as sensors and payloads change and evolve, different sample rate conversions are required. Not only do the input sample rates change as controllers evolve, but the requirements on Fout vary widely as different sensors or other payloads are incorporated on the UGV. Currently, the control software on the UGV is implemented monolithically as dedicated block of code including the SRC computation algorithms. SRC parameters are typically hard coded into the software. This necessitates re-writing and re-compiling the controller code every time the SRC needs to be changed. What is needed is a rapidly reconfigurable sample rate conversion method that allows rapid changes to the SRC parameters without requiring recompiling the control software.